‘Heat dome’ over Ontario and Quebec causing wild weather across much of Canada

TORONTO — Blame the heat dome hanging over Ontario and Quebec for some of the strange weather hitting other parts of the country.

Environment Canada meteorologist Julien Pellerin says scorching temperatures over the eastern part of the continent are causing below-normal temperatures in other regions, which have led to warnings of wet snow and heavy rain in the West.

“If you have a heat dome on a sector, you can expect colder air in another sector, so that’s what the Prairies are currently experiencing,” Pellerin said on Sunday.

“It’s coming from the United States, a high-pressure system that doesn’t move quickly … so it brings intense heat and moist air over southern Ontario and southern Quebec and it’ll settle there for the next three days.”

The dangerous temperature levels span from southwestern Ontario towards North Bay, Sudbury and Timmins, while in Quebec the highest temperatures are expected from Montreal to Shawinigan and north up to Abitibi.

Pellerin says he expects Ontario and Quebec to hit their peak daytime highs on Monday and Tuesday with temperatures rising above 30 C, and the humidex making it feel more like 40 to 45 degrees, depending on the region.

“It won’t last very long,” he added. “By the end of Tuesday and Wednesday, we will have a transition in air mass all over Canada, especially over Quebec and Ontario.”

Environment Canada warned of possible thunderstorms and tornadoes in northern parts of Ontario on the weekend. A dangerous storm ripped through the Mattawa area in northeastern Ontario late Saturday night, which caused the closure of Highway 17 between Bonfield and Mattawa.

Ontario Provincial Police said in a news release Sunday evening they helped evacuate approximately 290 people from two provincial parks in the area due to the storm, and the neighbouring Municipality of Calvin issued a state of emergency Sunday afternoon, warning residents in a social media post to avoid unnecessary travel due to downed trees, power lines and washouts disrupting local roads.

Other parts of the country, meantime, are seeing surprises from the heat dome.

On Saturday, Environment Canada warned that areas in British Columbia could face heavy showers, and over some of the highway summits, the possibility of wet snow.

Heavy rainfall advisories that had been in effect in southern Alberta were all lifted by Sunday, but the region received significant precipitation. City residents were being warned to stay off the Bow River.

The Calgary Fire Department advised against boating and all other water activities on the Bow due to higher-than-normal water flow, although the city said flooding over riverbanks was not expected.

“We know that Calgarians love their rivers, yet we also know that when our waterways flow this high and fast, there’s significant risk to anyone, regardless of your watercraft or skill level,” Calgary Fire Deputy Chief Pete Steenaerts said in a news release.

Saskatchewan’s Water Security Agency warned the Alberta rain could also lead to increased flows on the South Saskatchewan River between the Alberta boundary and Lake Diefenbaker.

The agency said Alberta began dumping water from reservoirs this past week to make room for the additional run-off.

It expected lake levels at Lake Diefenbaker, a large reservoir northwest of Regina that’s a popular recreation area, to rise over a metre this week as a result of the weather system.

Heat levels in Ontario and Quebec led Environment Canada to remind people to stay hydrated by drinking water before they’re thirsty, to watch for early signs of heat exhaustion and not overexert themselves.

“Be careful; you know yourself,” Pellerin said.

“Make sure you’re aware of what you’re feeling and take breaks, Make sure you have a location where you can rest with the air conditioning.”

In Quebec, schools are being urged to stay vigilant with the rising temperatures.

In a letter from the assistant deputy education minister, schools were encouraged to “put in place all the preventive measures you judge necessary to ensure everyone’s security.”

“Depending on the situation, these measures could go all the way up to closing one or more schools for the day of June 23,” said the message signed by Stephanie Vachon.

This report by The Canadian Press was first published June 22, 2025.

David Friend, The Canadian Press